Terry J. Reedy <tjre...@udel.edu> added the comment:
After looking at the doc chapter, I get that 'if __name__' block is needed on
Windows.
OK. batch mode with if __name__ block:
testmp.py
---------
print('Top of Module')
class C:
def f(s): print('Method C.f')
if __name__ == '__main__':
print('Start of main block')
import multiprocessing
p = multiprocessing.Process(target=C.f, args=(C(),))
p.start()
p.join()
command-prompt..\python32> python @misc2\testmp.py
output (similar to that of OP):
Top of Module
Start of main block
Traceback (most recent call last):
File "C:\Programs\Python32\lib\pickle.py", line 679, in save_global
klass = getattr(mod, name)
AttributeError: 'module' object has no attribute 'f'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "@misc2\testmp.py", line 9, in <module>
p.start()
File "C:\Programs\Python32\lib\multiprocessing\process.py", line 130, in start
self._popen = Popen(self)
File "C:\Programs\Python32\lib\multiprocessing\forking.py", line 267, in
__init__
dump(process_obj, to_child, HIGHEST_PROTOCOL)
File "C:\Programs\Python32\lib\multiprocessing\forking.py", line 190, in dump
ForkingPickler(file, protocol).dump(obj)
File "C:\Programs\Python32\lib\pickle.py", line 237, in dump
self.save(obj)
File "C:\Programs\Python32\lib\pickle.py", line 344, in save
self.save_reduce(obj=obj, *rv)
File "C:\Programs\Python32\lib\pickle.py", line 432, in save_reduce
save(state)
File "C:\Programs\Python32\lib\pickle.py", line 299, in save
f(self, obj) # Call unbound method with explicit self
File "C:\Programs\Python32\lib\pickle.py", line 623, in save_dict
self._batch_setitems(obj.items())
File "C:\Programs\Python32\lib\pickle.py", line 656, in batch_setitems
save(v)
File "C:\Programs\Python32\lib\pickle.py", line 299, in save
f(self, obj) # Call unbound method with explicit self
File "C:\Programs\Python32\lib\pickle.py", line 683, in save_global
(obj, module, name))
_pickle.PicklingError: Can't pickle <function f at 0x00B4B4B0>: it's not found
as __main__.f
C:\Programs\Python32>Top of Module
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "C:\Programs\Python32\lib\multiprocessing\forking.py", line 370, in main
self = load(from_parent)
EOFError
The essential problem seems to be the attempt to pickle the method attribute of
the class as a class attribute of the module.
----------
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue11969>
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